This invention relates generally to composite materials, and more particularly, to composite materials based on rigid polyurethane foams and reinforcing mineral fillers.
Polyurethane foams are commonly prepared by reacting isocyanate with hydrogen-containing compounds having reactive hydroxyl groups, for example, polyester or polyether polyols. The reaction occurs in the presence of a catalyst, and a blowing agent is provided in order to produce an expanded, cellular product. The blowing agent can be produced chemically by the interaction of the isocyanate with water to generate CO2 gas. In low density, high expanding systems, a blowing agent such as trichlorofluoromethane is added which vaporizes at the outset of the reaction. Polyurethane foam systems are commonly prepared as two components, the isocyanate component being maintained separate from the polyol-catalyst-blowing agent component until the time of use.
Structural articles formed from polyurethane foams usually include fillers to increase the strength of the polyurethane foam. U.S. Pat. No. 4,661,533 to Stobby describes a rigid polyurethane modified polyisocyanurate foam containing fly ash as a filler that is used for building insulation. However, structural building products, for example synthetic lumber, require higher density foams than those taught by Stobby.